Preparation of an oxidation catalyst



United States Patent 2,961,441 PREPARATION OF AN OXIDATION CATALYST Wendell W. Waterman, Arlington Heights, lll., assignor to Publiclter Industries, Inc., Philadelphia, Pa., a corporation of Pennsylvania No Drawing. Application January 28, 1953 Serial No. 333,822

4 Claims. (Cl. 252-463) This invention relates to a useful oxidation catalyst and to a process for its preparation, and more particularly to a highly active and selective catalyst for use in catalyzing the oxidation of olefins to olefin oxides, such as the oxidation of ethylene to ethylene oxide and the process for preparing such a catalyst.

This application is a continuation-in-part of my earlier application U.S. Serial No. 21,745, filed April 17, 1948 and now abandoned.

The advent of a variety of recent commercial processes involving olefinic hydrocarbons, such as the various cracking processes in the petroleum refining arts, has made a large amount of low molecular weight normally gaseous olefins such as ethylene available. It is desirable to convert these low molecular olefins to more economically valuable compounds and in recent years large scale efforts have been expended in this direction.

In particular, efforts have been undertaken to oxidize these olefins into their corresponding oxides. The olefin oxides are valuable compounds per se, as solvents, extractants, fumigants, insecticides and the like. Moreover, they are valuable intermediates for the preparation of a wide variety of useful organic compounds such as alcohols, glycols, aldehydes, carboxylic acids, ethers, esters, alkyloamines, resins, polymers and the like.

The commercial oxidation processes have conventionally involved oxidation of olefins in the presence of an oxidation catalyst such as silver, and extensive research on the development of superior silver oxidation catalysts has been undertaken. However, the vast majority of conventional silver oxidation catalysts have not proven fully satisfactory, and olefin oxidation processes using such catalysts have not been productive of adequate yields of olefin oxide.

A variety of processes have been developed to prepare such catalysts. For example, one such process is disclosed in US. Patent 2,040,782 to A. J. van Peski which issued on May 12, 1936. The catalyst used in this process is prepared by the thermal decomposition of a solid thermally-decomposableorganic silver compound to elemental silver. Thus, the silver salt of a low molecular weight organic carboxylic acid, such as silver oxalate is prepared, such as by the separation of precipitated silver oxalate from an aqueous solution, and then the solid silver salt is decomposed to elemental silver by the application of heat. The elemental silver catalyst thus obtained may be commingled with particles of an inert carrier to increase its volume or more preferably, utilized per se, as the oxidation catalyst.

Numerous other methods have been proposed for preparing silver oxidation catalysts and a wide variety of silver oxidation catalysts have been prepared. Thus, catalysts comprising silver deposited upon carriers or supports such as silica gel and pumice have been recommended, but these catalysts have been found to promote formation of extensive amounts of undesirable gaseous by-products such as carbon dioxide, when utilized for the oxidation of olefins. Aluminum oxide has also been ice recommended as a support material. However, there are certain forms of this compound, such as those known as the beta and gamma forms, which when impregnated with silver by conventional procedures, exhibit little if any catalytic activity for the oxidation of olefins. Alpha aluminum oxide has also been recommended as a carrier for catalysts used in the oxidation of olefins. However, I have found that many forms of alpha alumina do not comprise valuable carriers for olefin oxidation processes ,An object of my invention is to provide a highly active and selective catalyst for the oxidation of olefins to olefin oxides.

Another Object of my invention is to provide a method for the preparation of a highly active and selective catalyst for the oxidation of olefins to Olefin oxides.

These and other objects are accomplished by my invention. The process of my invention is: a method for preparing a highly active and selective catalyst for use in the oxidation of olefins to olefin oxides. The process of my invention comprises impregnating a carrier selected from the group consisting of alpha alumina and silicon carbide with an auqeous solution of a water soluble silver salt of a relatively low molecular weight organic carboxylic acid. It is essential for the purposes of my invention that the carrier have an average porosity of at least 35 and preferably from 35 to 65%. While any such water soluble silver salt capable of forming concentrated aqueous solution having upwards: of about 20 weight percent of dissolved salt can be used, silver lactate has been found to be most useful for the aforementioned purpose, especially when cmployed in the form of an aqueous solution having a weight percent concentration of the order of to After the impregnation, the impregnated carrier is dried and heated for a time sufficient to remove the anionic constituent of the silver salt, and to deposit elemental silver in a highly active form upon the surface and throughout the pores of the carrier. A temperature of up to about 425 C., and preferably about 350 C. to 425 C. is most advantageous for effecting the aforementioned drying and heating. Moreover, it is preferable to effect the drying and heating in an atmosphere of an inert gas incapable of supporting combustion such as nitrogen or the gases of the zero group of the periodic table, although the heating can be effected in air. However, all gases incapable of supporting combustion under the aforementioned conditions of thermal decomposition are not equally desirable. For example, I have obtained consistently inferior results when effecting the thermal decomposition in the presence of reducing gases such as hydrogen.

The highly active and selective catalyst useful for the oxidation of olefins to olefin oxides of my invention comprises from about 3 to 30 weight percent of elemental silver distributed upon the surface and throughout the pores of a carrier selected from the group consisting of alpha alumina and silicon carbide. It is essential for the purposes of my invention that the carrier have an average porosity of at least 35% and preferably from 35 to 65%.

As heretofore mentioned, the nature of the carrier employed in the preparation of the catalyst of my invention is of prime importance in procuring a catalyst capable of functioning efficiently. In the case of alumina l have discovered that the alpha form alone of the allotropic forms of alumina is useful for my purposes. Alpha alumina is prepared by heating aluminum oxide to a temperature which is capable of effecting a substantially complete conversion to the alpha form, i.e., a temperature of about 1500 C. to a temperature of about or slightly in excess of 2050 C. Moreover, I have found that only those alpha aluminas and silicon carbides having an average porosity of at least 35%, preferably 35% to 65%, comprise useful carriers for the preparation of the cat alyst of my invention. This porosity must consist largely of intercommunicating pores and should not be merely sealed-off bubbles. I

In the preparation of the catalysts of my invention,

care should be taken to avoid the introduction of appre- 5 and most preferably within the range 230 to 280 C. ciable quantitities of iron or chromium compounds such Thus, for example, in the oxidation of ethylene to ethylas the oxides of these metals, inasmuch as their presence ene oxide, a gaseous mixture comprising ethylene and a tends to increase the amount of carbon dioxide formed gas comprlsing molecular oxygen, such as air, is conduring the oxidation of ethylene. Such objectionable matacted with the aforementioned oxidation catalysts at a terials can most advantageously be removed by washing temperature of the order of 230 to 280 C. with the the carrier with a solution comprising a low molecular ethylene being present in said mixture in a concentration weight organic acid, such as lactic acid or a solution of of about 2% to 5%, preferably about 3.5% to 4%. The lactic acid. In particular, I have found that washing contact-time of the gas mixture with the catalyst under the carrier with a 20 to 30 weight percent hot lactic' such conditions should preferably be under eight secacid solution materially aids in the preparation of a valends, with a preferred contact-time comprising between uable oxidation catalyst. After the acid washing the two and seven seconds. The ethylene oxide thus procarn'er should be washed with water, until the washings duced can be isolated in a known manner and the reare substantially neutral. Moreover, the catalyst of my mainder of the eifiuent gases from the process vented to invention need not contain the usual promoting trace the atmosphere, or if deemed desirable, recycled. materials such as various compounds of the alkali metal The catalysts of my invention can be used in any of group, since these promoting trace materials do not imthe conventional catalytic procedures. For example, prove to any appreciable degree, if at all, the catalyst's when the catalyst is particulated to a mesh size of about iii i 80 mesh and smaller, the fluidized catalytic mode of oper- The impregnation of the catalyst is preferably effected ation can be utilized. Thus, the catalyst particles can at an elevated temperature. Thus, for example, when a be disposed in the form of a fluid bed, that is as a bed 50% to 65% silver lactate solution is used as the imof fine particles suspended in the olefin and molecular pregnating solution, a temperature within the range of oxygen reactant gases in the so-called fluidized state. 100 C. to 150 C. and preferably between about 120 In this state the suspended particles undergo the phenomand 130 C. is to be preferred. The carrier should reenon of hindered settling, and also, exhibit many of the main immersed in the solution for an extended period, properties of a boiling liquid. If desired, the fluidized such as 2 to 10 hours, and preferably from about 2% to particles can be transferred by means of a conduit from 4 hours. At the end of this period, the solution of the silone reactor to another. ver salt is drained off, and the wet impregnated carrier is Another procedural mode of operation that can be placed in an externally heated tube or muffle furnace, utilized with the catalyst of my invention involves the and dried and heated at a temperature of from about 350 disposition of the oxidation catalyst particles in the form C. to 425 C., and preferably from about 390 to 410 C. of a statlonary fixed bed. Thus, the particles can be During this heating period which is generally continued for packed in either a single bed or if desired in a plurality of from about 10 to 30 hours, and preferably from about 12 beds, and the olefin and molecular oxygen passed through to 16 hours a gas such as air or more preferably an inert the bed or beds at the oxidizing conditions. gas such as nitrogen is continuously introduced into the As illustrative of my invention, a number of catalysts furnace at a rate suflicient to remove the gaseous decomwere prepared in accordance with the procedures outposition products. The catalyst material thus obtained lined above, under the conditions specifically listed in has a silver content of from about 3 to 30% and prefer- Table 1 below, and then used as a catalyst for the oxidaably between about 5 and 12%. tion of ethylene in admixture with air to ethylene oxide It is desirable that the aforementioned heating to deunder the conditions specified in Table 1 below. The compose the silver salt be conducted at a temperature not oxidation was effected in each case in a reactor tube havin substantial excess of 425 C. I have found that at ing an internal diameter of 0.82" and being 3 in length, temperatures much in excess of this temperature level, mounted vertically within an enclosing jacket in which a i.e., 450 C. and above, the activity of the catalyst obsuitable heat transfer medium was employed to remove tained is substantially reduced. the heat of reaction.

Table 1 Impreg-natlon Decomposition Operation Oxidation Results Operation Percent Carrier Percent o 11 Yi ld,

Ag Lae- Time Tom Atmos- F ed Temp. Contact Percent c 01H 0 on Time Temp. tateln (hr-s.) 0. phere Catalyst 0. Time 0.11m 0,11. Feed (1118-) 901M101! (5608.) Feed 23; Percent of Theory 273 as as as ss RA-QBLY-IOI LP. ring pelas 125 sea is}! 400 N. 3.0 m as as 00 so lets. 211 as as w 54 27s as as 01 I so Bil-9s Alundum I (porous 8.0 125 65.6 15 400 N, 0.9 m 4.8 as 90 se aggregate). 276 8. 6 3. 5 93 57 260 6.8 as 9'! Do 3.0 125 56.7 us 400 N: 7.2 {g g a g am as as 9s, 55 m as as to 53 Do 3.0 125 56.2 8 400 N: 9.2 284 4.8 8.6 07 264 as as as so sso 4.3 as s4 s1 Do 3.0 56. 7 15 400 001...--- 6. 6 248 4. 3 8. 5 94 50 zas as as so so a: t3 t: s a Do 3.0 125 54.5 15 400 Alr 8.9 m u u 92 50 27s as as 01 st a a a a as T-71 Corundum' (porous 3.0 125 56.6 15 895 Air 10.0 271 3.5 m gate) as l. l I. 5 96 53 Table 1Continued Impregnation Decomposition Operation Oxidation Results Operation P t ereen Carrier Percent Ag in cm Yield,

Ag Lac- Timo Tern Atmos- Finished Tem Contact Percent Con CIHAO on Time 'Iem tete in (hrs) C. phere Catalyst C. Time CiHi in slow I 4 Feed (hrs) C. Solution (Bees) Feed remain P iirfient of eory 5. 2 3. 5 77 26 T-72 Corundum 4 (porous 3.0 125 56. 15 400 Air 8. 5 251 4. 8 3. 5 60 26 aggregate). 265 4. 3 3. 5 65 32 270 5. 3 3. 5 86 43 RC-Crystolon (porous 113- 3. 5 130 64. 1 400 N: 8.3 4. 3 3. 5 78 47 gregate-silioon carbide). 272 3. 6 3. 5 77 41 252 0. 4 3. 5 89 43 Aloxite (alpha alumina pel- 3.0 125 55. 0 17 400 ML--. 10. 5 254 5.3 3. 5 87 47 lets). 12. 0 3. 5 94 54 264 5. 3 3. 5 32 17 #38 7 (alpha alumina) 3. 5 125 56. 1 15 400 .Air.-- 8. 5 261 4. 3 8. 5 20 18 6. 6 3. 5 37 23 211 12. 0 3. 5 100 0 AL-l 5 (aluminum oxlde) 2. 0 100 55.0 9 400 All 7. 5 212 9. 4 3. 5 100 0 214 6.6 3. 5 100 0 9. 4 3. 5 87 50 Silicon Carbide i (cylindrical 2. 0 125 59. o 20 400 Air 14.7 $3 2:; 2 2 g; i: 275 o. 6 a. 5 so 44 1 A grade oi alpha alumina formed catalyst carrier sold by the Norton Corn ny of Worcester Mass. (hollow rings $6" diameter by 540" length; average porosity of 42% to 45%; and having the following compositions: 85.5% Ali :4, 12.1% 810;, 0.5 0 F940;, 0.2% MgO, 0.2% CaO, 0.4% N830, and 0.3%

A grade of alpha alumina 4 to 8 mesh particles sold by the Norton Company of Worcester, Mass. (average porosity of 42% to 45%; composition same as RA98LX10).

1 A grade of alpha alumina 4 to 8 mesh particles sold by the Aluminum Ore Company of East St. Louis, Illinois (average porosity of 55% to 75% and having the following compositions: 99.5% A1103, 0.02% NaiO, 0.02% SlOz, and 0.035% Fez03+Ti0:).

I Identical with T-7i except that average porosity is 25% to 5 A grade of silicon carbide in the form of porous aggregate 4 to 8 mesh sold by the Norton Company of Worcester, Mass. (average porosity of to 60% and having the following composition: 83.5% SiC, 10% S102, 4.9% A1203, 0.4% F6101, 0.2% MgO, 0.2% 02.0, 0.3% NarO, 0.2% K20, and 0.3% Ti z).

0 A grade of alpha alumina in the form of cylindrical pellets 54 e" in diameter by 54 0" ion average porosity to having the following composition: 79.3% AliGi; 13.0% SiOi, 2.7% silicates of Fe, Al, Mg, K, Na, and Ti sold by the orundum Co. oi Perth Amboy, NJ.

1 A grade of alpha alumina sold by the Norton Co. of Worcester, Mass; average porosity 2% to 5% and having the following composi '1: 99.46% A1203, 05% B102. .02% F9203, 04% T102, 0.35% NBzO-l-IQO.

B A grade of alumina consisting chiefly of the gamma form with a small proportion of beta alumina sold by the Harshaw Chemical Co. of Cleveland, Ohio; average porosity 41% to 48% and having the following composition: 98% A1103, 0.75% N820, 0.04% F8203, and 0.2% SiOr.

A grade of silicon carbide in the form of cylindrical pellets M a" in diameter by 965 long; average porosity 40% to 45% having the following composition: 77.5% SiC, 6.4% A1103, 14.6% SlOE, and 1.5% of Fe Al, Ti, Mg, N a, and K silicates. Sold by the Carborundum Co. of Perth Amboy, NJ.

10 Two hrs. 125 0., two hrs. 200 0., thirteen hrs. 400 0.

It is seen from the foregoing that the ethylene oxidawith an aqueous solution of lactic acid, washing the alpha tion runs using the catalysts of my invention namely those alumina thus treated with water until the washings are in which the silver has been impregnated on a. carrier substantially neutral, impregnating the Washed alpha aluconsisting of alpha alumina or silicon carbide having an 40 mine with a 50 to 65 aqueous solution of silver lactate, average porosity in excess of 35%, furnished vastly sudrying and heating the impregnated alpha alumina at a Perior results W116i! compared with Similar utilizing temperature of about 350 to 425 C. in an atmosphere Catalysts P p in the idfmtical i from Camus of an inert gas for a time sufficient to remove the anionic having either a lower P W consisting of beta constituent of the silver lactate and to deposit elemental and gifmma forms of l 45 silver in a highly active form upon the surface and While I have described 111 some detail the preferred emthroughout h pores f h l h l i bodiments of my invention, and certain variations thereof, A process f preparing a highly active and Selective f 13 to understood thahsuch for the Purposes of catalyst for use in catalyzing the oxidation of olefins to illustration and that the invention is not to be regarded l fi oxides which comprises washing an alpha alumina as limited to the details a .nd procedure herein described. 5 having an average porosity of between 35 and 65% with Q other hand the mention to regarfied an aqueous solution comprising between about 20 to 30% l p l by terms of clalms i lactic acid, washing the alpha alumina thus treated with which it is my intention to claim the novelty inherent in water until the washings are substantially neutral impreg my invention as broadly as possible in view of the prior nating the washed alpha alumina with a 50 65% art. a I

queous solution of silver lactate, drying and heating i descnbed my mvemlon what.I clam as F the impregnated alpha alumina at a temperature of about and desire to protect by Letters Patent is the following. 350 to C in an atmosphere of an inert gas for a l. A process for preparing a highly active and selective catalyst for use in catalyzing the oxidation of olcfins i Sumclent remove i amomc cqnstmient the silver lactate and to deposit elemental silver in a highly to olefin oxides which comprises washing an alpha alumina having an average porosity of between 35 and acme farm upon. the Surface and throughout tha pores of the alpha alumina.

% with an aqueous solution of lactic acid, washing the alpha alumina thus treated with water until the washings In a method l p paring a highly act} ve and selective catalyst composition for use in catalyzing the oxidaare substantially neutral, then impregnating the so prepared alpha alumina with an aqueous solution of silver 65 of ethylene to ethylene made, the whlcl? lactate, drying and heating the impregnated alpha alumina Pnse thorouglly washing an alpha alumina hfwmg at a temperature below about 425 C. for a time sufiicient avFrage f of between 35% and 5 wlth to remove the anionic constituent of the silver lactate and acldi was hmg the thus treated with f to deposit elemental silver in a highly active form upon the washmgs are substantially lfeutralg thereafter lmpreg' the surface and throughout the pores f he alpha nating the washed alpha alumina with a 50% to 65% 1 i aqueous solution of silver lactate, drying and heating the 2. A process for preparing a highly active and selcc- S0 impregnated alpha alumina at about C- in live catalyst for use in catalyzing the oxidation of olcfins to olefin oxides which comprises washing an alpha alumove the anionic constituent of said silver salt, ther y mine having an average porosity of between 35 and 65% leaving free silver in a highly active form deposited upon an atmosphere of an inert gas for a time suflicicnt to re alumina.

Rcfennces Cited in the file of this patent UNITED STATES PATENTS Van Peski May 12, 1936 Ovox'hcfl Ian. 5, 1943 Evans July 23, 1946 Voorhies Sept. 24, 1946 Finch at al July 15, 1947 Heidelet a1. Ian. 4, 1949 Aries July 26, 1949 

1. A PROCESS FOR PREPARING A HIGHLY ACTIVE AND SELECTIVE CATALYST FOR USE IN CATALYZING THE OXIDATION OF OLEFINS TO OLEFIN OXIDES WHICH COMPRISES WASHING AN ALPHA ALUMINA HAVING AN AVERAGE POROSITY OF BETWEEN 35 AND 65% WITH AN AQUEOUS SOLUTION OF LACTIC ACID, WASHING THE ALPHA ALUMINA THUR TREATED WITH WATR UNTIL THE WASHINGS ARE SUBSTANTIALLY NEUTRAL, THEN IMPREGNATING THE SO PREPARED ALPHA ALUMINA WITH AN AQUEOUS SOLUTION OF SILVER LACTATE, DRYING AND HEATING THE IMPREGNATED ALPHA ALUMINA AT A TEMPERATURE BELOW ABOUT 425* C. FOR A TIME SUFFICIENT TO REMOVE THE ANIONIC CONSTITUENT OF THE SILVER LACTATE AND TO DEPOSIT ELEMENTAL SILVER IN A HIGHLY ACTIVE FORM UPON THE SURFACE AND THROUGHOUT THE PORES OF THE ALPHA ALUMINA. 